Evaluation of palatal dimensions in different facial patterns by using digital dental casts

ABSTRACT Objective: To analyze the variations of hard palate volume in adults with normal occlusion and different facial types and patterns, by using a three-dimensional analysis on digital casts. Methods: The dental casts of 70 Caucasian adults (28 men, 42 women), mean age of 16.4 years (SD 1.3 years), were scanned by using a tridimensional scanner (Delcam PowerSHAPE™, 2010, Birmingham, UK). Close points were selected in the gingival and cervical regions on the lingual surface of the maxillary teeth, to analyze palatal morphology. The facial patterns and types, and the measurements (width, length, height, volume) of the space on the hard palate were compared using analysis of covariance (ANCOVA), with age as the covariate, and sex as the independent variable. The significance level of 5% (p < 0.05) was adopted. Results: This study showed that the measurements of the width and length were similar among the mesofacial, dolichofacial and brachyfacial facial types, although the height and volume of the space on the hard palate were slightly smaller in dolichofacial individuals, and both Pattern I and Pattern II individuals showed no significant changes for the four measurements. The mean values among facial patterns were: Pattern I - width 38.31±2.59 mm; length 37.44±2.42 mm; height 17.03±2.42 mm and volume 10.52±1.72 mm3; Pattern II - width 37.48±2.44 mm; length 37.48±2.44 mm; height 16.79±2.42 mm and volume 10.41±1.65 mm3 (p>0.05 for all variables). Conclusion: There were no significant differences for the facial patterns and facial types of the individuals compared in the analyzed sample.


INTRODUCTION
When examining an orthodontic technique, it is important to determine the mechanics and the consequences of its use, as well as its impact on the anatomical structures of the stomatognathic system. The lingual technique is extremely attractive from an aesthetic perspective, because it is considered "invisible" -as the brackets are positioned on the lingual surface of teeth. On the other hand, this technique is sometimes disregarded by potential users, due to several reasons, including: fear of tongue pain or of developing changes in speech, especially for patients in certain professions, such as speakers and those with artistic careers.
The first study describing the use of lingual brackets positioned on the lingual surface of teeth and a mushroom-shaped archwire for tooth correction was presented by Fujita 1

in 1979.
At the end of the 1970s, this technique was also being developed in the United States. 2 The fact that the brackets were in direct contact with the tongue muscle drew the attention of professionals and patients, causing fear that the lingual appliance could cause pain. However, studies 3,4 showed that adaptation to the lingual appliance is similar to that with the buccal orthodontic technique, and patient reports showed that some individuals could adapt more quickly than others, which may be related Kairalla SA, Velasco L, Bachi ALL, Yamamoto LH, Cappellette Jr M -Evaluation of palatal dimensions in different facial patterns by using digital dental casts 5 to the size of the dental arches, the position of the tongue and its relationship with the dental arches and, especially, the hard palate. Adaptation may also be related to the type of lingual bracket, how the lingual appliance is mounted, and the shape of the archwire used. Studies show that patients adapt to lingual appliances within three weeks, [3][4][5] and the type of bracket used has a direct relationship with the patient's adaptation to speech, comfort and painful symptoms. Furthermore, a higher bracket profile due to either the bracket's metallic structure (bracket base) or its combination with resin to form a pad in individual bracket mountings, results in greater discomfort for the patient. 6,7 The tongue is a muscle that is in direct contact with the hard palate and the lingual surface of teeth during swallowing and articulatory and chewing movements. 8 Thus, some researchers have analyzed the width, length, height and volume of the hard palate 9 because it has a close relationship with the tongue, not only during speech and chewing movements, but also during swallowing and resting, when the tongue remains supported on the structures of the hard palate and the lingual surface of the maxillary teeth for a long period of time.
Three-dimensional (3D) digitized models have enabled examination 10 Kairalla SA, Velasco L, Bachi ALL, Yamamoto LH, Cappellette Jr M -Evaluation of palatal dimensions in different facial patterns by using digital dental casts 6 In addition, the hard palate, as part of the fixed scaffold of the skull, may be related to the facial patterns and facial types of individuals, which has led some researchers to investigate this correlation. [14][15][16][17] Thus, the present study aimed to determine the width, length,  The following inclusion criteria were used: individuals with normal natural occlusion, complete dental eruption, except for the third molars, and the presence of four occlusion keys. 19 The four keys considered were a Class I molar relationship,  After the points were defined, they were joined in the anterior and posterior regions, to delimit the space where the tongue could be positioned comfortably at rest on the structures of the hard palate (Fig 1). Delcam PowerSHAPE™ 2010 software tools were used to determine the width, length, height and volume of that space on the palate. First, the program selected and marked with a rectangle the area to be analyzed (Fig 2).
Next, the program cut the selected area. This delimited area is shown in the Figure 3. Subsequently, these measurements were tabulated in EXCEL (Microsoft™, Redmond, Washington, USA) for statistical analysis.

STATISTICAL ANALYSIS
Descriptive statistics, including means, standard deviations, and 95% confidence intervals (95% CI) were calculated for the mea- The normality of the data was evaluated using the Shapiro-Wilk test, whose results led to the conclusion that the variables studied had a normal distribution. To compare facial patterns (Table 1) and facial types (Table 2) with the width, length, height and volume of the space of the palate, analysis of covariance (ANCOVA) was used, with age as the covariate and sex as the independent variable. In all statistical tests, a significance level of 5% (p < 0.05) was adopted.   (p > 0.05).

DISCUSSION
The 3D technology used in the present study is an effective tool 9-12,20 and less invasive than cone beam computed tomography 21 , and it is probably more accurate than measurements of the transversal space of the hard palate in a linear manner, i.e., 2D measurements obtained based on the cusps of teeth. 14,22 The morphology, size and shape of the palate were investigated in a longitudinal study spanning ten years in adult patients, using similar landmarks in the palate as those used in the present study. 9 The results suggested that the shape of the hard palate for the distance between the lingual surface and the bracket base on these irregular surfaces 11,12,26,27 will be greater in areas where more compensation is necessary. In these cases, the brackets may advance into the space occupied by the tongue, resulting in possible patient discomfort. 6 Some brackets may be mounted with a resin pad, and others may be mounted without a pad. A bracket base close to the lingual surface will have a lower profile, and the appliance will invade less of the space occupied by the tongue. Therefore, the patient will have better adaptation in terms of speech and comfort. The results of this study showed that the space of the palate height (16.17 mm) and volume (9.58 mm 3 ) were slightly smaller in dolichofacial individuals ( Most studies using 3D technology to assess the dimensions of the hard palate were related to treatments for palatal disjunction 11,12,20,21 and/or mouth-breathing in young patients, 31,32 reinforcing that malocclusion may play a role in facial architecture. The present study used models from a sample of individuals with normal natural occlusion, and the results can serve as parameters for future research on biomechanics, configurations and lingual arch shapes, [8][9][10][11][12][23][24][25][26][27]

CONCLUSION
There were no correlations between facial Patterns I and II or the dolichofacial, mesofacial and brachyfacial facial types and the width, length, height or volume of space on the hard palate.